Navigation devices that acquire a current position and provide various kinds of guidance have been widely used.
Such navigation devices come in a variety of forms, such as a navigation device provided exclusively for vehicle, a navigation device that is realized by incorporating a navigation function as one function into various kinds of terminal devices such as a smart phone, etc.
Navigation devices in such variety of forms are common in an aspect of, in order to acquire a current position, including a GPS receiver that receives radio waves from GPS satellites (hereinafter, referred to as GPS radio waves) and acquiring the current position on the basis of the received GPS radio waves.
However, in case of acquiring the current position only using GPS radio waves, the current position cannot be acquired in blocking areas, in which GPS radio waves are not receivable, for example, in tunnels, in buildings' shadow, under bridges, etc. Therefore, navigation devices incorporated into vehicles are configured to be able to continuously acquire the current position by further supplementarily using a vehicle speed sensor, a gyro sensor, a geomagnetic sensor, etc.
For example, Patent Document 1 describes a technology that, in a case in which positioning by a GPS becomes unable, acquires the current position in tunnels with a simple configuration in which only a speed sensor is utilized without a directional sensor, while in a conventional technology, the current position is acquired by a dead reckoning system using a vehicle speed sensor and a directional sensor.
In such a manner, navigation devices capable of utilizing the vehicle speed in addition to a GPS can estimate the current position in tunnels using the vehicle speed and time in a case in which the tunnels have only one exit.
However, in a case in which a tunnel has a branch and therefore there are two or more exits, it is not possible to determine the road on which the vehicle is traveling after passing the branch.
On the other hand, in case of navigation devices whose functions are realized by various kinds of terminals such as smart phones that are used independently from the vehicle, neither a direction nor a vehicle speed can be utilized. Therefore, the current position cannot be determined in tunnels regardless of whether a branch exists or not.
In addition, some vehicles include a function that provides the vehicle speeds to terminal devices with or without wires. However, even when the vehicle speeds are acquired from those vehicles, it is not possible to determine a road on which each vehicle travels after passing a branch in a tunnel, as is the case in Patent Document 1.